Cyclotron able to accelerate at least two types of particles

Abstract

The present invention relates to a dual-frequency resonant cavity ( 6 ) for cyclotron which includes a dee ( 10 ), a pillar ( 20 ), and a conducting enclosure ( 40 ) surrounding the pillar and the dee, an end of the pillar being connected to the base of the conducting enclosure and an opposite end of the pillar ( 20 ) supporting the dee ( 10 ). The conducting enclosure and the pillar form a transmission line comprising at least three portions ( 20 a , 20 b , 20 c ), each portion having a characteristic impedance (Z c1 , Z c2 , Z c3 ). The characteristic impedance Z c2 of the intermediate portion ( 20 b ) is substantially lower than the characteristic impedances Z c1 et Z c3 of the two other portions ( 20 a , 20 b ), which makes it possible to have the cavity resonate according to two modes in order to produce two distinct frequencies, without having to make use of moving components such as for example sliding short-circuits or mobile plates. The present invention also relates to a method for designing such a resonant cavity, based on the use of electromagnetic—and radio frequency simulation tools.

The invention claimed is: 
     
       1. A resonant cavity adapted for the acceleration of charged particles in a cyclotron, comprising a dee, a pillar and a conducting enclosure surrounding at least partially said pillar and said dee, an end of said pillar supporting the dee, the conducting enclosure and the pillar thus forming a transmission line, characterized in that an opposite end of said pillar is mechanically fixed and electrically connected in a fixed way to a base of the conducting enclosure, and in that the linear capacity of an intermediate portion of the transmission line located between the aforementioned ends of the pillar is larger than the linear capacity of the other portions of said transmission line that are located between the aforementioned ends of the pillar. 
     
     
       2. A resonant cavity according to  claim 1 , characterized in that the linear capacity of the intermediate portion of the transmission line is larger than twice the linear capacity of the other portions of said transmission line that are located between the aforementioned ends of the pillar. 
     
     
       3. A resonant cavity according to  claim 2 , characterized in that the linear capacity of the intermediate portion of the transmission line is larger than ten times the linear capacity of the other portions of said transmission line that are located between the aforementioned ends of the pillar. 
     
     
       4. A resonant cavity according to  claim 1 , characterized in that the characteristic impedance (Z c2 ) of the intermediate portion and the characteristic impedances (Z c1 , Z c3 ) of the other portions of the transmission line are such that the cavity is capable of resonating according to two modes in order to produce two distinct frequencies in a substantially double ratio. 
     
     
       5. A resonant cavity according to  claim 1 , characterized in that the pillar comprises several superimposed cylinders, one of these cylinders corresponding to said intermediate portion of the transmission line and having an average diameter which is substantially larger than the average diameter of anyone of the other cylinders. 
     
     
       6. A resonant cavity according to any of  claims 1  to  5 , characterized in that the conducting enclosure comprises several superimposed hollow cylinders, one of these hollow cylinders corresponding to said intermediate portion of the transmission line and having an average diameter which is substantially smaller than the average diameter of anyone of the other hollow cylinders. 
     
     
       7. A resonant cavity according to any of  claims 1  to  5 , characterized in that it furthermore includes a tuning capacitor comprising a mobile electrode connected electrically to the conducting enclosure, placed opposite the pillar and substantially at the level of the intermediate portion of the transmission line.